In recent years, as large screen sizes have become common for home television receivers, flat-screen display devices have rapidly become popular as a replacement for conventional Cathode Ray Tube (CRT) devices. Along with liquid crystal displays, the main type of display device with a large, flat screen is a plasma display panel (hereinafter referred to as a PDP), which achieves luminescent display by causing plasma discharge to occur in minute cells corresponding to pixels and converting the emitted ultraviolet radiation into visible light via phosphors.
In a PDP, the most common method currently used to cause a plasma discharge in the cells is a method referred to as AC surface discharge.
In a typical structure for an AC surface discharge PDP, barrier walls referred to as ribs are provided between two glass substrates (a front substrate and a back substrate) to establish a gap of a fixed distance, so that a discharge space enclosed by the two glass substrates is formed in this gap. A discharge gas is injected into the discharge space, and rows of parallel electrode pairs are formed on the surface of the front substrate facing the discharge space, each electrode pair being formed by a scan electrode and a sustain electrode. Furthermore, an insulating layer is formed on the electrode pairs. Data electrodes are provided on the back substrate in a position perpendicular to the electrodes on the front substrate. The data electrodes are covered by an insulating layer.
In a PDP with this structure, applying voltage between the scan electrodes and the sustain electrodes creates a plasma discharge by causing the discharge gas in the discharge cells to undergo breakdown. At this point, since an insulating layer is formed on the scan electrodes and the sustain electrodes, the electric charge produced by the discharge accumulates on the surface of the insulating layer, offsetting the potential of the electrodes. As a result, when voltage is applied, a discharge occurs in the form of a pulse, and a wall charge accumulates. When the applied voltage reverses, however, the wall charge overlaps with the reversed applied voltage due to having the same polarity, and therefore the applied voltage necessary for sustaining discharge reduces. By controlling this wall charge, discharge in the discharge cell can selectively be turned on or off, thus allowing for image display.
Conventionally, PDPs emit ultraviolet light using xenon, which has a relatively high ionization and excitation voltage. Therefore, the power efficiency of conversion of input power into useful ultraviolet light is an extremely low value of 10% or less. Accordingly, efforts have been made to increase the luminous efficiency of PDPs. As described in Patent Literature 1 and 2, the composition of the discharge gas has been examined.
For example, Patent Literature 1 discloses increasing the partial pressure of xenon in the discharge gas while increasing the overall pressure of the discharge gas. This is an attempt to improve the ultraviolet light source not by increasing the resonant radiation (wavelength of 147 nm) from excited xenon atoms, but rather by using light over a broad spectrum focusing on 172 nm radiation from xenon excimers.
An excimer is formed by a three-body reaction between an excited xenon atom and xenon atoms in the ground state, as in the following formula.Xe*+Xe+Xe→Xe2*+Xe  Formula 1Therefore, as the xenon partial pressure increases, the probability of formation rapidly increases. Furthermore, since xenon in the ground state has a repulsive potential, the excimer rapidly dissociates into single atoms without the occurrence of self-absorption. A high luminous efficiency is thus obtained even at high gas pressure.
Recent years have seen an increase in high-definition television broadcasts, such as a high-vision form of digital terrestrial broadcasting, leading to a desire for high-definition display devices. To achieve high definition, pixel size necessarily decreases. A decrease in pixel size, however, leads to a relative increase in plasma wall-loss due to an increase in bipolar diffusion. This causes the discharge voltage to rise and significantly lowers brightness and luminous efficiency. Accordingly, there is a desire for further improvement in luminous efficiency, particularly in PDPs with a small cell size.
[Citation List]
Patent Literature
Patent Literature 1: Japanese Patent Application Publication No. 2002-83543
Patent Literature 2: Japanese Patent Application Publication No. 2007-249227